Harmonic enhanced load traction system

Abstract

The application provides a harmonic enhancement type load traction system, which comprises a circulator, an impedance tuner, a high-pass filter, a radio frequency power amplifier and a non-reflection duplexer which are connected in series to form a closed loop structure; the input end of the circulator is connected to a bias structure of a device under test, and the non-reflection duplexer is connected to a fundamental wave signal to form an open loop structure; the application uses an active closed loop load traction structure at the harmonic and an active open loop load traction structure at the fundamental wave, effectively compatibilizes the tuning of the fundamental wave and the second harmonic, has high integration, and can realize the impedance tuning of the harmonic without introducing a signal source and other devices.

Description

Technical Field

[0001] This invention relates to the field of power amplifier design, and more particularly to a harmonic-enhanced load traction system. Background Technology

[0002] With the development of modern communication technology, power amplifiers, as core components in the field of radio frequency communication, have faced higher requirements in terms of efficiency and gain. Load pulling has proven to be an effective method to improve these performance indicators, providing a means to present the device under test (DUT) to a non-50Ω environment and measure its performance. This provides designers with the information needed to match network design to obtain optimal DUT performance and has been successfully demonstrated to reduce design risk and save time in the product design cycle.

[0003] Due to its relatively simple structure, low cost, and good power handling capability, passive load pulling technology is currently widely used in the market. It is a combination of a central conductor and a tuning probe, generating arbitrary impedance through changes in the relative position between the central conductor and the ground wire to achieve load modulation. However, due to its inherent structural defects, passive load pulling cannot be applied to broadband impedance matching and harmonic matching. Therefore, active load pulling technology was proposed. Because of its larger tuning range compared to passive load pulling, it has been widely used in the characterization of microwave devices. Depending on the structure, it can be divided into two types: closed-loop active load pulling and open-loop active load pulling, such as... Figure 1 As shown.

[0004] Passive load pulling is prone to wear and tear due to its mechanical structure, resulting in system losses and significantly reducing calibration accuracy. Furthermore, the lack of active components prevents the synthesis of high reflection coefficients and coverage of the Smith chart edges, making it unsuitable for harmonic load pulling. Active load pulling offers unparalleled speed advantages over passive load pulling. However, both mainstream approaches—closed-loop and open-loop active load pulling—require high-gain, high-linearity amplifiers to ensure high system accuracy and a wide tuning range, significantly increasing system cost. While the former offers higher test throughput, it carries the risk of self-oscillation, potentially damaging components; the latter avoids this risk but requires complex iterative algorithms. Additionally, implementing active load pulling requires a separate signal source for each frequency, increasing system cost and complicating system setup, hindering its large-scale industrial application. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention provides a harmonic-enhanced load traction system that is compatible with the tuning of the fundamental and second harmonics, has a high degree of integration, and can achieve harmonic impedance tuning without introducing other equipment such as signal sources.

[0006] To achieve the above objectives, the present invention provides a harmonic-enhanced load traction system, comprising: a circulator, an impedance tuner, a high-pass filter, an RF power amplifier, and a reflectionless duplexer connected end-to-end to form a closed loop structure; the input end of the circulator is connected to the bias structure of the device under test, and the reflectionless duplexer is connected to the fundamental signal to form an open loop structure.

[0007] Preferably, the circulator includes a first circulator and a second circulator connected in sequence. The first end of the first circulator is connected to the output end of the bias structure of the device under test, and the second end is connected to the input end of the non-reflective duplexer. One end of the second circulator is grounded.

[0008] Preferably, the reflection-free duplexer includes a first directional coupler, a low-pass filter, and a second directional coupler connected in sequence; the isolation terminal of the first directional coupler is connected to the output terminal of the RF power amplifier, the coupling terminal of the second directional coupler is grounded, and its through terminal is connected to the fundamental signal source.

[0009] Preferably, when a harmonic signal passes through the non-reflective duplexer, the harmonic signal is input from the isolation terminal of the first directional coupler and output from the input terminal to the output terminal of the bias structure of the device under test; when a fundamental signal passes through, the fundamental signal is input from the fundamental terminal of the second directional coupler and output from the input terminal of the first directional coupler.

[0010] Preferably, the impedance tuner includes an adjustable attenuator and an adjustable phase shifter connected in sequence.

[0011] The advantages of the harmonic-enhanced load traction system provided by this invention are:

[0012] 1. This invention uses an active closed-loop load traction structure at the harmonic level and an active open-loop load traction structure at the fundamental level, effectively compatible with the tuning of the fundamental and second harmonics, and has a high degree of integration. It can achieve impedance tuning of harmonics without introducing signal sources or other devices.

[0013] 2. This invention uses a non-reflective duplexer to synthesize the fundamental and second harmonic waves, instead of a broadband combiner, which reduces losses in the load traction structure, lowers the requirements for the signal source in the open-loop structure, and avoids instability of the active load traction structure caused by signal reflection.

[0014] 3. By setting an impedance tuner, this invention broadens the frequency tuning range, making it easy to achieve higher harmonic tuning and obtain better test results. At the same time, it avoids the need for complex iterative algorithms and high-power, high-gain amplifiers in traditional load traction systems, saving time and instrument costs. Attached Figure Description

[0015] Figure 1 The existing technologies are: (a) an open-loop active load traction system, and (b) a closed-loop active load traction system.

[0016] Figure 2 This is a structural diagram showing the connection between the harmonic-enhanced load traction system and the power amplifier bias structure provided by the present invention.

[0017] Figure 3 The structural diagram of the reflection-free duplexer in the harmonic-enhanced load traction system provided by the present invention;

[0018] Figure 4 The simulation schematic diagram of the harmonic-enhanced load traction system provided by this invention;

[0019] Figure 5 The simulation results of the harmonic-enhanced load traction system provided by the present invention based on ADS are shown in the figure, where (a) is the tuning range of the fundamental load reflection coefficient and (b) is the tuning range of the second harmonic load reflection coefficient. Detailed Implementation

[0020] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, unless otherwise specified, the following embodiments and features described therein can be combined with each other.

[0021] like Figure 2 As shown, the present invention provides a harmonic-enhanced load traction system, which includes: a circulator, an impedance tuner, a high-pass filter, an RF power amplifier, and a reflectionless duplexer connected end to end to form a closed loop structure; the input end of the circulator is connected to the bias structure of the device under test, and the fundamental signal is connected to the reflectionless duplexer to form an open loop structure.

[0022] Specifically, this invention employs a closed-loop structure formed by connecting a circulator, impedance tuner, high-pass filter, RF power amplifier, and reflectionless duplexer end-to-end. This allows the input harmonic signal to be fed back to the harmonic input terminal via feedback, preventing re-injection of echoes that could cause loop oscillations and burn out components, thus improving system stability. Furthermore, a fundamental signal source is connected to the reflectionless duplexer, forming an open-loop structure. By combining open-loop and closed-loop structures, this invention allows the system to simultaneously accommodate tuning and matching of the fundamental and harmonic signals without adding a harmonic signal source, widening the tuning range. It replaces the passive load-driven, easily worn mechanical structure, improving high precision while ensuring tuning accuracy, reducing system cost, and simplifying system complexity.

[0023] In this embodiment, the circulator includes a first circulator and a second circulator connected in series. The first end of the first circulator is connected to the output end of the bias structure of the device under test, and the second end is connected to the input end of the non-reflective duplexer. One end of the second circulator is grounded.

[0024] In this embodiment, the circulator is a unidirectional transmission device. In actual use, the first end of the first circulator receives the harmonic signal output from the bias structure of the device under test. After transmission through the first circulator, the signal is output to the second circulator. The second circulator is used to suppress interference in the harmonic signal and reduce system loss. It should be noted that using two circulators can completely suppress interference in the harmonics. Increasing the number of circulators will increase the loss in the system loop structure and reduce the tuning accuracy and efficiency. Conversely, reducing the number of circulators will fail to suppress interference generated in the harmonics, and similarly, the tuning accuracy of the harmonics will also decrease. Therefore, the number of circulators cannot be arbitrarily increased or decreased. In another embodiment, the circulator can be any microwave device with signal direction selection function, such as a four-port coupler.

[0025] In this embodiment, the impedance tuner includes an adjustable attenuator and an adjustable phase shifter connected in sequence. The adjustable attenuator is used to adjust the amplitude of the frequency, and the adjustable phase shifter is used to adjust the phase of the signal. The impedance tuner changes the gain of the harmonic signal by adjusting the frequency and phase, avoiding the need for complex iterative algorithms and high-power gain amplifiers, thus saving time and instrument costs.

[0026] In this embodiment, the system also includes a high-pass filter and an RF power amplifier connected in series with the impedance tuner. The high-pass filter is used to remove low-frequency interference signals in the harmonics. The harmonic signal (second harmonic) is filtered and then amplified by the RF power amplifier before being output to the load terminal of the device under test.

[0027] In this embodiment, the device under test (DUT) is preferably a power amplifier. Its bias structure includes: a signal generator, a first power amplifier, a second coupler, the DUT, the second coupler, and the second power amplifier connected in sequence. Both the first and second power amplifiers include a capacitor and an inductor. One end of the inductor is connected to one end of the capacitor, and the other end is connected to a DC current source. The other end of the capacitor is connected to the first port of the first circulator and the signal generator, respectively. The first and second couplers are connected to a vector network analyzer.

[0028] like Figure 3 As shown, the reflection-free duplexer includes a first directional coupler, a low-pass filter, and a second directional coupler connected in sequence; the isolation terminal of the first directional coupler is connected to the output terminal of the RF power amplifier, the coupling terminal of the second directional coupler is grounded, and its through terminal is connected to the fundamental signal source.

[0029] Specifically, both the first and second directional couplers have a gain of 3dB. A low-pass filter is connected between the coupling terminal of the first directional coupler and the input terminal of the second directional coupler. Similarly, a low-pass filter is also connected between the through terminal of the first directional coupler and the isolation terminal of the second directional coupler. The low-pass filters are used to filter the fundamental signal passing through the reflectionless duplexer, improving the stability of the fundamental signal. In another embodiment, the reflectionless duplexer can be replaced by a reflectionless filter.

[0030] In the closed-loop circuit, when a harmonic signal passes through the non-reflective duplexer, the harmonic signal is input from the isolation terminal of the first directional coupler and output from the input terminal to the output terminal of the bias structure of the device under test; when the fundamental signal passes through, the fundamental signal is input from the fundamental terminal of the second directional coupler and output from the input terminal of the first directional coupler.

[0031] Specifically, when the harmonic signal enters the reflectionless duplexer through the loop, it enters from the isolation terminal of the first directional coupler. Utilizing the 90° phase shift at the through terminal of the directional coupler, the reflected signals from the coupling and through terminals of the first directional coupler are 180° out of phase, thus canceling each other out. This prevents the reflected signal from returning to the input terminal. The loop signal is directly output from the input terminal of the first directional coupler back to the load terminal (the output terminal of the bias structure of the device under test). This avoids the re-injection of the reflected signal (the harmonic signal entering the reflectionless duplexer and then reflecting back to the input terminal), which could easily cause loop oscillation and burn out the device, ensuring the stability of the entire system and the accuracy of load pulling. Therefore, when the harmonic signal reaches the reflectionless duplexer, it passes through the barrier without entering, improving system stability.

[0032] When tuning the fundamental signal, the fundamental signal source provides the fundamental signal, which is input through the direct-through end of the second directional coupler. After being filtered by a low-pass filter, it is fed into the output end (load end) of the bias structure of the device under test through the input end of the first directional coupler, thus achieving tuning of the fundamental and harmonic signals. This method achieves signal isolation at the input end; that is, the harmonic signal is input from the first port of the first circulator, and the fundamental signal is input from the reflectionless duplexer. Furthermore, in traditional load traction systems, if control of harmonic signals is to be added in addition to control of the fundamental signal, an additional harmonic signal source needs to be introduced. The price of the introduced harmonic signal source increases with frequency, making it expensive for tuning at high harmonic frequencies. In this embodiment, the reflectionless duplexer enables the system to form a closed-loop structure at the harmonic frequency, achieving harmonic tuning. This invention can perform harmonic tuning and matching without introducing an additional signal source (i.e., a harmonic signal source), reducing system cost and simplifying system complexity.

[0033] In another embodiment, the structure of the present invention can be used to perform open-loop load pulling on harmonics (high frequencies) and closed-loop load pulling on the fundamental frequency. In other embodiments, the structure of the present invention is also used to realize source pulling (tuning at the source end).

[0034] In this embodiment, the principle of the open-loop structure at the fundamental frequency can be expressed as follows:

[0035]

[0036] in, Let a be the load impedance at the fundamental frequency. 2，1 For the fundamental signal at the second port of the incident wave, a g,1 The voltage wave provided by the signal generator at the load end of the device under test, k1 is the loss coefficient on the path from the signal generator to the output end of the device under test, b 2,1 The fundamental component of the output wave of the device under test and the input a g,1 The superposition of the resulting reflected waves can be calculated using the following formula:

[0037]

[0038] Where S1 is the fundamental component of the voltage wave signal output by the device under test, and Γ is the reflection coefficient of the output impedance of the device under test relative to the load (usually 50Ω).

[0039] In the closed-loop structure, the load impedance at the second harmonic can be obtained. for:

[0040] ,

[0041] In the formula, b 2,2 Let a be the second harmonic component of the output wave of the device under test. 2,2 This represents the second harmonic component of the input wave at the device output. To determine the real-time adjustment values ​​for the adjustable phase shifter and the injected signal, we can use the Mason formula from the signal flow graph:

[0042] ,

[0043] ,

[0044] ,

[0045] Combining the above formulas, we have:

[0046]

[0047] Where k2, k3, and k4 represent the losses or gains along each path, respectively. b is the phase that the adjustable phase shifter changes. x,2Let x be the harmonic signal of the x-th output port of the device under test, where x = 1 to 4.

[0048] like Figure 4 The diagram shows the simulation principle of the closed-loop structure and the open-loop structure of the present invention. The test environment is Genesys Harbec (HB) harmonic balance simulation, which simulates the signal injection at the load end from amplitude 0dBm to 30dBm and phase 0° to 360°. Figure 5 The figure shows the simulation results of the fundamental and second harmonic load reflection coefficient tuning range based on ADS in this invention.

[0049] Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

Claims

1. A harmonic-enhanced load traction system, characterized in that, include: The components are a circulator, an impedance tuner, a high-pass filter, an RF power amplifier, and a reflectionless duplexer, which form a closed-loop structure when connected end to end. The input of the circulator is connected to the bias structure of the device under test, and the fundamental signal is connected to the reflectionless duplexer to form an open-loop structure. The reflection-free duplexer includes a first directional coupler, a low-pass filter, and a second directional coupler connected in sequence; the isolation terminal of the first directional coupler is connected to the output terminal of the RF power amplifier, the coupling terminal of the second directional coupler is grounded, and its through terminal is connected to the fundamental signal source. When a harmonic signal passes through the non-reflective duplexer, the harmonic signal is input from the isolation terminal of the first directional coupler and output from the input terminal to the output terminal of the bias structure of the device under test; when a fundamental signal passes through, the fundamental signal is input from the fundamental terminal of the second directional coupler and output from the input terminal of the first directional coupler.

2. The harmonic-enhanced load traction system according to claim 1, characterized in that, The circulator includes a first circulator and a second circulator connected in sequence. The first end of the first circulator is connected to the output end of the bias structure of the device under test, and the second end is connected to the input end of the non-reflective duplexer. One end of the second circulator is grounded.

3. The harmonic-enhanced load traction system according to claim 1, characterized in that, The impedance tuner includes an adjustable attenuator and an adjustable phase shifter connected in sequence.

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